1. Wochenbericht AL510

Forschungsreise „Baltic GasEx“ FS Alkor AL510 03.06.2018 – 16.06.2018: Wochenbericht für den Fahrtabschnitt 03.06.18 – 09.06.1

Marines Isopren: Bildung, Emissionen und ihr Einfluss auf die Chemie in der Atmosphäre

Volatile organic compounds (VOCs) play an important role in influencing the oxidative capacity of the atmosphere. Isoprene, the most important biogenic VOC, has received increased attention in recent years as biogenic emissions of isoprene are the main contributor for secondary organic aerosols (SOA) formation. SOA in the atmosphere influence the radiative balance through scattering or absorption of solar radiation and, therefore, have a direct impact on the climate of our Earth’s system. The knowledge about the spatial and seasonal distribution of isoprene, as well as its production and consumption processes in the surface ocean, is still lacking and is crucial to quantify marine isoprene emissions. The main goal of this work was to increase the global dataset of marine isoprene measurements and provide a better understanding of the biogeochemical cycling in the surface ocean. This improved understanding was used to calculate the global surface isoprene distribution and the isoprene emission to the atmosphere in order to estimate the influence of marine isoprene on the Earth’s atmosphere and climate.Flüchtige organische Verbindungen (VOCs: volatile organic compounds) haben einen großen Einfluss auf die oxidative Kapazität der Atmosphäre. Isopren, als wichtigster Vertreter der biogenen VOCs, wurde in den letzten Jahren zunehmende Aufmerksamkeit zuteil, da es als wichtiger Vorläuferstoff für die Bildung von sekundären organischen Aerosolen (SOA: seconary organic aerosols) verantwortlich ist. In der Atmosphäre beeinflusst SOA durch Streuung und Absorption von Sonnenstrahlung die Strahlungsbilanz der Erde und hat somit einen direkten Einfluss auf das Klima. Ziel dieser Arbeit war es Messungen von Isopren im Ozean durchzuführen und die Prozesse sowohl zur Bildung als auch zum Abbau von Isopren im Oberflächenozean zu untersuchen. Die hieraus gewonnenen Erkenntnisse wurden genutzt, um sowohl die globale Konzentrationsverteilung von Isopren im Oberflächenozean als auch die resultierenden Emissionen in die Atmosphäre zu berechnen, und um somit schlussendlich den globalen Einfluss von ozeanischem Isopren auf das Klima der Erde abschätzen zu können

1.Wochenbericht AL516

Forschungsreise „Baltic GasEx“ FS Alkor AL516 12.09.2018 – 23.09.2018 Wochenbericht für den Fahrtabschnitt 12.09.18 – 16.09.1

Marine isoprene - Formation, emissions and their impact on the atmospheric chemistry

Volatile organic compounds (VOCs) play an important role in influencing the oxidative capacity of the atmosphere. Isoprene, the most important biogenic VOC, has received increased attention in recent years as biogenic emissions of isoprene are the main contributor for secondary organic aerosols (SOA) formation. SOA in the atmosphere influence the radiative balance through scattering or absorption of solar radiation and, therefore, have a direct impact on the climate of our Earth’s system. The knowledge about the spatial and seasonal distribution of isoprene, as well as its production and consumption processes in the surface ocean, is still lacking and is crucial to quantify marine isoprene emissions. The main goal of this work was to increase the global dataset of marine isoprene measurements and provide a better understanding of the biogeochemical cycling in the surface ocean. This improved understanding was used to calculate the global surface isoprene distribution and the isoprene emission to the atmosphere in order to estimate the influence of marine isoprene on the Earth’s atmosphere and climate

Seasonal study of the Small-Scale Variability of Dissolved Methane in the western Kiel Bight (Baltic Sea) during the European Heat Wave in 2018

Methane (CH4) is a climate-relevant atmospheric trace gas which is emitted to the atmosphere from coastal areas such as the Baltic Sea. The oceanic CH4 emission estimates are still associated with a high degree of uncertainty partly because the temporal and spatial variability of the CH4 distribution in the ocean surface layer is usually not known. In order to determine the small-scale variability of dissolved CH4 we set up a purge-and-trap system with a significantly improved precision for the CH4 concentration measurements. We measured the distribution of dissolved CH4 in the water column of the western Kiel Bight and Eckernförde Bay in June and September 2018. The top 1 m was sampled in high-resolution to determine potential small-scale CH4 concentration gradients within the mixed layer. CH4 concentrations throughout the water column of the western Kiel Bight and Eckernförde Bay were generally higher in September than in June. The increase of the CH4 concentrations in the bottom water was accompanied by a strong decrease in O2 concentrations which led to anoxic conditions favorable for microbial CH4 production in September. In summer 2018, northwestern Europe experienced a pronounced heatwave. However, we found no relationship between the anomalies of water temperature and excess CH4 in both the surface and the bottom layer at the site of the Boknis Eck Time-Series Station (Eckernförde Bay). Therefore, the 2018 European heatwave most likely did not affect the observed increase of the CH4 concentrations in the western Kiel Bight from June to September 2018. The high-resolution measurements of the CH4 concentrations in the upper 1 m of the water column were highly variable and showed no uniform decreasing or increasing gradients with water depth. Overall, our results show that the CH4 distribution in the water column of the western Kiel Bight and Eckernförde Bay is strongly affected by both large-scale temporal (i.e. seasonal) and small-scale spatial variabilities which need to be considered when quantifying the exchange of CH4 across the ocean/atmosphere interface

Marine isoprene production and consumption in the mixed layer of the surface ocean – A field study over 2 oceanic regions.

Parameterizations of surface ocean isoprene concentrations are numerous, despite the lack of source/sink process understanding. Here we present isoprene and related field measurements in the mixed layer from the Indian Ocean and the eastern Pacific Ocean to investigate the production and consumption rates in two contrasting regions, namely oligotrophic open ocean and the coastal upwelling region. Our data show that the ability of different phytoplankton functional types (PFTs) to produce isoprene seems to be mainly influenced by light, ocean temperature, and salinity. Our field measurements also demonstrate that nutrient availability seems to have a direct influence on the isoprene production. With the help of pigment data, we calculate in-field isoprene production rates for different PFTs under varying biogeochemical and physical conditions. Using these new calculated production rates, we demonstrate that an additional significant and variable loss, besides a known chemical loss and a loss due to air–sea gas exchange, is needed to explain the measured isoprene concentration. We hypothesize that this loss, with a lifetime for isoprene between 10 and 100 days depending on the ocean region, is potentially due to degradation or consumption by bacteria

The influence of air-sea fluxes on atmospheric aerosols during the summer monsoon over the tropical Indian Ocean

During the summer monsoon, the western tropical Indian Ocean is predicted to be a hot spot for dimethylsulfide emissions, the major marine sulfur source to the atmosphere, and an important aerosol precursor. Other aerosol relevant fluxes, such as isoprene and sea spray, should also be enhanced, due to the steady strong winds during the monsoon. Marine air masses dominate the area during the summer monsoon, excluding the influence of continentally derived pollutants. During the SO234-2/235 cruise in the western tropical Indian Ocean from July to August 2014, directly measured eddy covariance DMS fluxes confirm that the area is a large source of sulfur to the atmosphere (cruise average 9.1 μmol m−2 d−1). The directly measured fluxes, as well as computed isoprene and sea spray fluxes, were combined with FLEXPART backward and forward trajectories to track the emissions in space and time. The fluxes show a significant positive correlation with aerosol data from the Terra and Suomi-NPP satellites, indicating a local influence of marine emissions on atmospheric aerosol numbers